1. Field of the Invention
The present invention relates to an optical part for a camera and a method of fabricating the same.
2. Description of Related Art
In recent years, digital cameras and camera-equipped mobile-phones become widespread, and lower-cost and higher-precision lenses are required.
Examples of a lens material include glass and plastic. Since the glass has many species and is abundant in the variation of optical properties, its optical design is easy. Furthermore, since the glass is an inorganic material, it has high reliability and can fabricate a high precision optical part by polishing.
However, glass is high cost, and when an aspheric shape other than a plane or a sphere is formed, a lens has to be formed by use of a special polishing apparatus or by the so-called mold method in which a glass material capable of deforming at low temperatures is molded with an expensive and highly heat resistant mold (made of ceramic) or the like, and therefore production cost becomes high.
As a method of solving the above-mentioned problems, a compound optical part to obtain desired properties by laminating a resin layer on a glass substrate is proposed. In Japanese Unexamined Patent Publication No. 54-6006, a low pass filter, in which an organic polymer layer is formed on a plane glass substrate, is disclosed. In Japanese Unexamined Patent Publication No. 52-25651 and Japanese Unexamined Patent Publication No. 6-222201 and the like, the so-called compound aspheric lens, in which a resin layer having an aspheric shape is formed on a glass substrate, is disclosed.
However, these patents cannot respond to further reductions in cost since glass is used as a substrate. Therefore, it is conceivable to employ a plastic substrate, but a plastic generally has a hygroscopic property. For example, saturated water absorption of an acrylic resin was 2.0%, and that of an olefin resin is 0.1%. Accordingly, when the plastic substrate is employed, an olefin resin having a low water absorption rate is preferable, but when such an olefin resin is used as a substrate, a problem that the adhesion of the substrate to a resin layer to be formed on the substrate is low arises.